The self-adhesive, addition cross-linking silicone-rubber blends according to the invention are characterized by good adhesion to substrates without the necessity of special handling for the molds used for producing the molded parts, which makes possible release of the addition cross-linked silicone-rubber blends from the mold. In addition, generally no subsequent curing of the composite molded parts is necessary.
A series of methods have been suggested to achieve an adhesive bond between addition cross-linking silicone elastomers and their substrates. One option is the use of a so-called primer that is used for pretreatment of the substrate surface. This requires an additional step and handling of solvents during processing. Both are disadvantageous. Another option consists of achieving adhesion of addition cross-linking silicone elastomers to substrates by the addition of one or more additive to the non-cross-linked silicone-rubber blend.
One other variation provides for the production of a thermoplastic-siloxane blend in which different siloxanes are mixed into the thermoplastic matrix before molding and the surface of molded parts of this thermoplastic blend are bonded with an addition cross-linking silicone-rubber blend. U.S. Pat. No. 5,366,806 hereby claims hydrogen siloxane with an additional alkenyl group in the thermoplastic matrix that is connected with adhesion to addition cross-linked polyorganosiloxane rubber that can preferably contain other organic functional SiH adhesion promoters.
U.S. Pat. No. 5,366,805 discloses a polycarbonate that contains siloxane copolymers or terpolymers containing hydrogen siloxane with epoxy or aryl groups. U.S. Pat. No. 5,418,065 suggests, instead of a siloxane-containing thermoplastic, a polypropylene terpolymer that contains addition cross-linking polyorganosiloxane rubber and SiH siloxanes containing epoxy, that are bonded during cross linking. The adhesion occurs e.g. during 8 min at 120° C. In this process, the thermoplastic part is injected immediately before the application of the silicone-rubber. The system makes possible the mold release of the composite parts from a metal mold.
Another solution is the preparation of addition cross-linking polyorganosiloxane rubbers that contain one or more additives, depending on the type of thermoplastic substrate and that can be bonded on this thermoplastic under different conditions during cross-linking. In this process, it is desirable to bond especially thermoplastics with high softening temperatures with silicone-rubber and, in contrast, to keep the adhesion to metallic mold material, i.e. generally steel, as low as possible.
According to U.S. Pat. No. 4,087,585, for example a good adhesion to aluminum is achieved by the use of two additives, a short-chain polysiloxane with at least one SiOH group and one silane with at least one epoxy group and an Si-bound alkoxy group. According to J. Adhesion Sci. Technol., Vol. 3, No. 6, pp 463-473 (1989), good adhesion to various metals and plastics is achieved by addition of an epoxy silane in combination with a homopolymeric cross linker. In EP-A 875 536, an improved adhesion on various plastics is achieved by use of an alkoxysilane with an epoxy group and a hydrogen silane with at least 20 SiH functions per molecule, whereby these mixtures are also distinguished by improved reactivity.
EP 350 951 describes the use of a combination of acryl or methacryl alkoxysilane with an epoxy-functional silane and a partial allyl ether of a multivalent alcohol as an additive to achieve permanent adhesion of addition cross-linking silicone elastomers on glass and metal.
These mixtures have the disadvantage that they also exhibit good adhesion to metals and are thus problematic in processing with uncoated metal molds.
DE 199 43 666.5 discloses that, by addition of a combination of glycidoxypropyltrimethoxysilane and methacryloxypropyltrimethyoxysilane, a good adhesion to polyamide and polybutylenterephthalate is achieved by subsequent curing of the composite parts with easily mold release capability from uncoated steel molds. However, a relatively high quantity of silanes is used, and to achieve good final adhesion a subsequent curing of the composite molded parts is recommended, which involves an additional working step.
U.S. Pat. No. 4,082,726 discloses the use of a terpolymer, i.e. of a siloxane, that consists of at least 3 different siloxy groups. In addition to Si epoxy groups, this can include Si-phenyl, SiH and other siloxy units. These epoxy siloxanes are used in addition to the almost optional alkenyl siloxanes A) and one hydrogen siloxane B) in order to produce adhesion between a thermoplastic substrate and an addition cross-linking polyorganosiloxane. No preferred concentrations for the organic function units of silicon are disclosed. The presence of the terpolymer containing epoxy causes both a thermoplastic and a metal adhesion.
U.S. Pat. No. 5,405,896 discloses, instead of the siloxane terpolymers containing epoxy, a copolymer and/or terpolymer with at least one phenylene group containing oxygen and at least one SiH group. The silicone-rubbers are bonded to the thermoplastic surface, for example during 8 min at 120° C. The mold release is successful in a non-coated metal mold.
U.S. Pat. No. 6,127,503 suggests, instead of the siloxane copolymers and/or terpolymers containing oxygen, a terpolymer with at least one phenyl and/or phenylene unit, a nitrogen-containing unit and an SiH group. The silicone-rubbers are cured with adhesion to the thermoplastic surface, e.g. during 10 min at 120° C.
EP 686 671 (U.S. Pat. No. 5,536,803) describes the use of an organohydrogen polysiloxane as an additive, whereby at least 12 mol-% of the monovalent Si-bound organic radicals are aromatic groups. In this case, adhesion to ABS was actually found, which was not quantified, and an easy mold release capability with metallic surfaces; an evaluation of the typical technical thermoplastics, e.g. polyamide, polybutylene terephthalate or polyphenylene sulfide was not carried out. A specific application area for these thermoplastics was not seen. Also, no preferred range for the SiH content of the corresponding siloxane components was disclosed. The silicone-rubber was brought to adhesion to the thermoplastic surface, e.g. over 100 sec. to 8 min at 60-100° C. during cross-linking.
The object of the present invention is to provide addition cross-linking silicone-rubber blends with good adhesion on various substrates, especially technical thermoplastics with high softening temperature such as polyamide, polytbutylene terephthalate or polyphenylene sulfide without the necessity of the tools being coated or treated with mold separating agents for processing in an automatic injection molding machine to prevent adhesion to the tools and generally without the need for the composite parts to be subsequently cured. To do this, the target is additional components that are simple and can be manufactured cost-effectively for silicone-rubbers that can also be added separately as separate components into commercially known, preferably 2-component, rubber.